A great deal has changed since World War II submarine offensive
combat operations and Cold War intelligence, surveillance, and reconnaissance
(ISR). Many coastal nations have realized that a few capable nonnuclear
submarines—preferably air-independent propulsion (AIP) types (sometimes
referred to as “SSPs”) armed with antiship cruise missiles (ASCMs)—offer one of
the best options to provide credible, economical defense of their territorial
waters.

For countries that can afford them, modern nuclear attack submarines
can operate offensively in littoral waters extremely quietly without being
threatened by the majority of anti-access/area-denial (A2/AD) defensive
measures. They can penetrate such barriers essentially at will. A modern SSP
can hunker down at very slow speeds and become nearly impossible to find in a
classic broad-area, passive sonar antisubmarine warfare (ASW) search conducted
by an SSN.

In other words, the defending nation finds it difficult to keep
the offensive SSNs out, but those SSNs cannot find and engage the defensive
AIP/ASCM submarines that are keeping the surface warships and carriers out of
the A2/AD zone.

What’s a navy to do?

A
New Threat Environment

Although
the post–Cold War U.S. surface navy took some time to rediscover the idea of
fighting in the littorals, submariners never lost sight of it. Deep-ocean Hunt for Red October –type peacetime ASW events drew
the most attention, but the real bread-and-butter operations for U.S.
submarines involved covert ISR operations in Soviet coastal waters. 1 This
history of shallow-water ISR extends back as far as the pre–World War II period
when U.S. submarines closely watched the Japanese fortification of Pacific
islands. During the course of the Pacific war, many offensive submarine
operations were conducted in the shallow waters of the Pacific Rim inside of
what is often called “the first island chain.”

The be-all and end-all of the Cold War’s “Third Battle of the
Atlantic” (as Professor Owen Cote of the Massachusetts Institute of Technology
named it) was the United States’ and NATO’s “acoustic advantage.” At times, the
advantage was as great as 40 dB. In practice, this meant U.S. submarines could
hear activity at many tens of miles that the enemy could hear at one mile—a
nice edge to bring to a fight. That differential no longer exists, and even
though some edge against potential adversaries’ top-end nuclear and nonnuclear
submarines remains, it often translates into initial detection ranges measured
in hundreds of yards rather than miles.

The bad news is that modern, quiet submarines no longer have the
ability to sanitize a given geographic area of other modern, quiet submarines,
since the mean time to detect an adversary is unacceptably large, especially in
the littorals—waters shallower (often much shallower) than 100 fathoms, where
background noise and extremely quiet propulsion systems combine to make passive
sonar less effective than in the open ocean.

The good
news, however, is that adversary submarines face the same problem. A Virginia -class submarine can operate with relative
impunity within a denied area. Improvements in foreign subs mean a Virginia may not be as effective as a U.S. submarine
once would have been at antisubmarine warfare, but it can perform other types
of valuable mischief.

Successful
submarine employment in current and foreseeable scenarios will require a
“connectivity advantage” analogous to the Cold War acoustic advantage. The quantity of data passed is less important than the quality of the data—and its assurance throughout a
submarine’s operating envelope—and it will require the ability to disrupt the
other side’s connectivity.

The
Problem for Shallow-Water Defenders

Defensive submarine operations in shallow waters protect a
defender’s coastal waters from invasion. This invasion may take the form of an
amphibious landing or an attack on national assets from sea-based air power. In
any case, large surface ships and carriers must close the enemy coast.

Submarines playing defense may need to get close enough to the
surface ships to do their own targeting. In World War II, most successful
torpedo attacks were conducted from inside 2,000 yards, but modern torpedoes
permit attacks from greater than 20,000 yards. As a rule of thumb, if the
submarine can see the target, it can be attacked.

Surface ships possess highly developed close-in ASW detection
and engagement capabilities including effective periscope detection radars.
This leads to a problem for the defensive submarines. Submarines possess four
critical core capabilities—stealth, mobility, firepower, and endurance.
Nonnuclear submarines—even AIP ones—fall short in terms of mobility and
endurance if they must search for and close highly mobile targets such as
amphibious ready groups (ARGs) or carrier strike groups (CSGs).

An appropriate tactic for nonnuclear submarines on their
own—shallow—turf is to stay hidden and not move a lot, especially at noisy high
speed. The concept is suited perfectly to employment of long-range ASCMs: stay
in “hide” positions until the attack, move to a launch position, attack, then
quickly return to the hide. The weakness of this practice is that someone else
has to provide the ASCM-equipped submarine with near-real time targeting data.

The
Offense Does not Have It Easy, Either

For purposes of this discussion, offensive submarine operations
rest on several assumptions. First, the location to be attacked is far from the
homeports of the attacker. Second, the deployed submarines will have to operate
without logistical support for several months. Third, the waters to be
infiltrated might be extremely cold or extremely warm. And fourth, a timely
response is critical.

Large size and significant power for air conditioning and
life-support equipment greatly enhance the platform’s ability to reach distant
waters, whether arctic or tropic, and remain for extended periods. This helps
explain a recent trend in nonnuclear submarines designs toward the
3,000–3,500-ton displacement range as opposed to approximately 1,000 tons, the
standard just a short time ago. But even the large ones do not compete in all
aspects with nuclear submarines.

The core values of stealth, mobility, firepower, and endurance
are most fully embodied in nuclear-powered attack and guided-missile (SSGN)
submarines. These boats possess the range to cross oceans and the stealth to
penetrate A2/AD defenses.

Even so, the SSNs or SSGNs cannot easily take the fight to the
stealthy, hidden AIP submarines. And the defensive submarines pose the last,
most potent A2/AD threat to the surface ships that wish to attack the territory
the AIP boat is defending.

What
a Navy Can Do

The threat these unlocated defending submarines pose to surface
ships must be eliminated or at least severely mitigated. The vulnerability lies
in the means by which these defenders receive targeting data from nodes on
shore. The opening round of offensive ASW actions should be land-attack strikes
from the SSNs and -SSGNs against these nodes, as well as on targeting assets
such as over-the-horizon radar sites (including secondary strikes on radars
that pop up after the primary sites are taken down). In this regard, this
“suppression of enemy submarine connectivity” is analogous to the familiar suppression
of enemy air defenses integral to any air campaign.

It is
interesting, but not entirely surprising, that dependence on connectivity (or
mission degradation in the absence of it) varies as a function of submarine
type. That is, the more capably a submarine platform can use mobility and/or
endurance to compensate for late or inaccurate intelligence, the less it
depends on off-hull support. Additionally, the bigger a platform is and the
greater discretionary electrical power it has for sensors and computer
processing of raw data, the more it is likely to become a source for rather than a user of an
information grid.

Two key assumptions support the concept that disrupting
shore-based targeting facilities and their connectivity to offshore submarines will
substantially neuter a modern A2/AD complex. The most critical assumption is
that adequate command and control connectivity will be maintained with the
penetrating SSNs and SSGNs. The other is that the defensive submarines largely
will be incapable of effectively operating autonomously because of the large
size of the A2/AD area that results from defending against long-range
land-attack cruise missiles.

The U.S. submarine force owns a long history of having to
function effectively in an independent role with limited means to ask for or
receive guidance from their masters ashore. This has resulted in a necessary
skill set that emphasized the technique—the art—of submarine warfare. It
required an extensive apprenticeship to develop.

Modern
technology provides very large “pipes” through which to pass two-way data,
information, and knowledge. It also enables a more procedural manner of
submarine warfare, a tempting scheme for countries with smaller navies.
Technology therefore permits these platforms to be effective while manned with
less experienced crews—so long as this high bandwidth connectivity is not
disrupted.

More
Data, More Risk

If highly trained U.S. submarine forces can continue to resist
the temptations associated with having these large pipes available and actively
maintain the techniques required to operate effectively in a degraded command,
control, communications, computers, and intelligence environment, then both of
the above assumptions should remain true.

Offensively
oriented submarines typically have more options for connectivity due to their
larger size, available power, and redundancy in equipment. But properly operated
they should be less dependent on connectivity than
smaller and power-limited defensively oriented submarines.

This dichotomy provides favorable options for the offensive
platform and highlights a defensive vulnerability to be exploited—all while
playing to an offensive strength. Keeping SSPs moving by forcing them to do
more of their own ISR and targeting exposes them to the maximum danger from the
offensively minded SSNs and SSGNs while also consuming their limited AIP
capability. Cutting off the data tether to the land increases the chances SSPs
will surrender the advantage of silence and make the kind of noise that only
motion induces. An underwater submarine duel makes for great movies—but it is
not how the Navy will win a submarine battle in the littorals.

1. A
substantive examination of these operations is contained in Sherry Sontag and
Christopher Drew, Blind Man’s Bluff: The Untold Story of
American Submarine Espionage (New York: PublicAffairs, 2016).

Captain
Patton served on two SSBNs and five SSNs, commanding the USS Pargo (SSN-650). He also served in the Office of the
CNO in submarine research and development, as the chief staff officer and
deputy for readiness and training at Submarine Development Squadron 12, as the
director of tactical training at Naval Submarine School, and as the director of
wargaming systems at the Naval War College. He now consults on matters of
stealth warfare, sensors, weapons and communications. He served for three years
as the technical consultant to Paramount Pictures for the film The Hunt for Red October .

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